Compressible flexographic printing plate construction

ABSTRACT

The present invention relates to an improved compressible flexographic printing plate that uses a compressible layer comprising a polyurethane (meth)acrylate resin and microspheres. The process of the invention produces a chemically fused printing plate that eliminates the need for an adhesive to secure the compressible layer to the back of the printing plate.

FIELD OF THE INVENTION

The invention is directed to a method of making a compressibleflexographic printing plate having an improved compressible foam layer.

BACKGROUND OF THE INVENTION

Flexographic printing is widely used in the production of newspapers andin the decorative printing of packaging media. Numerous photosensitiveprinting plate formulations have been developed to meet the demand forfast, inexpensive processing and long press runs.

Photosensitive printing elements generally comprise a support layer, oneor more photosensitive layers, an optional slip film release layer, andan optional protective cover sheet. The protective cover sheet is formedfrom plastic or any other removable material that can protect the plateor photocurable element from damage until it is ready for use. The slipfilm may be disposed between the protective cover sheet and thephotocurable layer(s) to protect the plate from contamination, increaseease of handling, and act as an ink-accepting layer.

Flexographic printing plates desirably work under a wide range ofconditions. For example, they should be able to impart their reliefimage to a wide range of substrates, including cardboard, coated paper,newspaper, calendared paper, and polymeric films such as polypropyleneand the like. Importantly, the image should be transferred quickly andwith fidelity, for as many prints as the printer desires to make.

To prepare a printing plate with typical commercially availableequipment, an image-bearing transparency or negative, i.e., atransparent film having opaque regions corresponding to the reverse ofthe image which one desires to impart to a printing plate, is placed ona glass platen, and covered with a transparent, polymeric cover film.The transparency and cover film are secured by vacuum to the platen, anda layer of photopolymerizable resin laminated to a backing sheet isplaced on the cover film. Actinic radiation is shined through the glassplaten toward the backing sheet. The regions of the resin which areimpinged by the actinic radiation undergo polymerization or “curing” toform a cured resin that is insoluble in a solvent used for washing awayuncured regions of the photopolymer to “develop” or reveal the reliefimage in the cured resin.

The regions of the resin layer which were protected from the actinicradiation by the opaque regions of the transparency are washed awayusing a developer solution. The cured regions are insoluble in thedeveloper solution, and so after development a relief image formed ofcured photopolymerizable resin is obtained. The cured resin is likewiseinsoluble in certain inks, and thus may be used in flexographicprinting. The liquid photopolymerizable resin may also be exposed toactinic radiation from both sides of the resin layer.

Compressible materials have found great utility in flexographicprinting, particularly in the printing of corrugated stock or similarsubstrates that have an uneven, deformable surface. With suchsubstrates, the printing plate must be flexible so that it will conformto the uneven surface and evenly deliver a coating of ink thereon.However, if the plate is too soft or flexible, the image on the platewill distort under the pressure used to contact the plate with thesubstrate, and thus will not transfer the image with the desiredfidelity.

Compressible printing plates are also useful in:

-   -   A. printing on wide webs (films of cellophane, polyethylene,        polypropylene, polyester, vinyl and paper having a web thickness        in the range of about 0.5 to 5 mils to overcome sag and        distortion and machine gauge variation by the compressibility of        foam.    -   B. printing safety papers (checks, bond and stock forms) with        even uniform constant tone in background print.    -   C. process printing (4 color printing) where uniformity of ink        laydown is critical to proper color development.

Compressible printing plates also have a longer life. The mechanicalshock to the plate, in each print motion, causes a gradual wearing ofthe relief, gradually leading to loss of sharpness in print. Thecompressible layer absorbs the mechanical shock leaving the reliefprinting surface relatively unaffected (minimal flattening ordistortion) resulting in longer plate life.

Mounting a printing plate onto a compressible layer allows for thatlayer to deform and compress with the substrate, while the printingplate can then be made to withstand the rigors of direct contact withthe substrate. The alternate approach involves making the printing platesofter, which can lead to an undesirable growth of the characters underthe required printing impression pressure, particularly when printing onrough or uneven stock or on presses with uneven impression and/or platecylinders.

On their own, high durometer plates can often damage the deformablesubstrate during the printing process. However, a higher durometerplate, in combination with a base compressible layer, can potentiallysolve both of these issues. In this way, one can use a fairly hard, i.e.high durometer, plate which will not provide a distorted image, and takeadvantage of the compressibility of the foam backing to allow the plateto bend and flex, and thereby contact all regions of an unevensubstrate. Typical compressible layers consist of foamed materials,oftentimes polyurethane or other thermoplastic materials, and are oftenlaminated to the back of a cured image-bearing printing plate using tapeor other pressure sensitive adhesives.

A persistent problem with this approach however is that it is verydifficult to secure the foam materials to the back of the plate. It isdifficult to apply the adhesive uniformly, and foam materials exhibitthe problem that they stretch during mounting to the plate and, ifstabilized, cause buckling when the plate is flexed. In addition, thesesteps are time consuming, and therefore can be quite costly to the tradeshops, mounters, and printers who are getting the plate ready for press.The extra backing layer can also actually interfere with the truecompressibility of the plate construction.

In most cases, the printing plate is already completely exposed anddeveloped before the compressible layer is secured thereto, althoughseveral examples exist wherein liquid or uncured solid photopolymericmaterials are cast and directly exposed on top of the compressiblelayer. However, in all of these processes, the compressible layer isstill formed in a separate step and then pretreated with an adhesive orsome sort of tie coat layer to laminate the compressible layer to theprinting plate.

U.S. Pat. No. 5,325,776, to Rather, Sr. et al., describes the use ofpolyurethane foam materials as compressible layers to be used in concertwith a flexographic printing plate. However, the polyurethane foam isnot UV-curable and requires a coating of an adhesive layer on top of thefoam to secure the foam to the printing plate.

U.S. Pat. No. 5,894,799 to Bart et al., describes the use of anelastomeric photopolymer as the compressible layer, wherein theelastomeric photopolymer contains open cells on the surface to createthe compressible nature. Photopolymerization is used only to create theopen cells, and an adhesive layer is still required in theplate-laminating step. The compressible layer must then be pre-exposed,developed, and post-cured prior to being adhered to the printing plate.In addition, the elastomeric photopolymer of the compressible layer is astyrenic block copolymer-based photopolymer, not a polyurethane, andthus requires solvent development.

U.S. Pat. No. 5,962,111 to Rach, describes the casting of a liquidphotopolymer layer onto a compressible material with open cells, andthen insufficiently curing that layer to allow it to serve as a tie coatfor the printing plate layer. A second coating of liquid resin is thencoated on top of the pre-cured layer, and the plate is exposed anddeveloped. In this instance, the compressible layer is required to haveopen cells, and is pre-treated with the resin of choice for making theprinting plate. In essence, the photopolymer is serving as its ownadhesive. Again, this system requires multiple steps until the finalsystem is in place.

As is readily seen, while various methods have been suggested in theprior art for preparing compressible flexographic printing plates, thereremains a need in the art for a simple manufacturing process forpreparing compressible photopolymer plates that overcomes theshortcomings of plates made according to prior art methodologies.

The purpose of the present invention is to provide a one-step system forthe production of compressible printing plates using conventional platemaking methods and materials. Utilizing a photocurable resin, such as apolyurethane (meth)acrylate resin that contains thermoplasticmicrospheres, a compressible foam can be created and cast along with thefirst photocurable layer in which the relief image is formed and twolayers cured simultaneously to form the compressible plate system of theinvention. The one-step process of the invention eliminates the need foradhesives to lamination the compressible layer to the back of theexposed printing plate.

Furthermore, while most urethane foams are actually created during thepolymerization step or by post-curing/blowing of the urethane, thepresent invention does not require any alteration of the urethane, onlya blend of the final resin with the microspheres.

U.S. Pat. No. 6,287,638 to Castelli et al., describes the use ofthermoplastic microspheres in the formation of printing blankets. Themicrospheres are dispersed into a thermoplastic medium and thenvulcanized using heat to form a crosslinked matrix. The surface of theblanket is then cast on top of the surface of a carcass material.However, this is a non-ultraviolet curing system and is also amulti-step system, require a separate compressible layer-formation stepbefore the printing element is ready to be used. Adhesion in thesesystems often requires the use of a tie coat layer to affix the printinglayer on top of the compressible layer. Often times, the microspherelayer is covered with layers of fabric, so that the printing layer doesnot come into contact with the compressible layer per se, but rathercomes into direct contact only with the fabric.

SUMMARY OF THE INVENTION

It is an object of the present invention to minimize the time it takesto ready a compressible flexographic printing plate for press usage.

It is another object of the present invention to eliminate the need foran adhesive layer between the printing plate and the compressible layerin the compressible printing plate system.

To that end, the present invention is directed to an improvedcompressible relief image printing plate comprising:

a) a cover film;

b) a photocurable layer directly on the cover film; and

c) a photocurable compressible layer directly on the photocurable layer,the photocurable compressible layer comprising a polyurethane(meth)acrylate resin with thermoplastic microspheres uniformly dispersedtherein;

wherein the photocurable layer and the compressible layer aresimultaneously cured to create a chemically fused system.

The invention is also directed to a method of preparing a compressiblerelief image printing plate comprising the steps of:

-   -   a) securing a photographic negative to a glass platen, wherein        the photographic negative has opaque areas corresponding to a        reverse of a desired relief image;    -   b) covering the photographic negative with a transparent cover        sheet;    -   c) creating a bi-layer photocurable system on the cover sheet by        casting a photocurable layer on the cover sheet and then casting        a photocurable compressible layer directly on top of the        photocurable layer;    -   d) exposing the bi-layer photocurable system to actinic        radiation through the photocurable compressible layer to cure        the photocurable compressible layer and a portion of the        photocurable layer to create a cured floor in the photocurable        layer;    -   e) exposing the bi-layer photocurable system to actinic        radiation through the photographic negative to form the relief        image in the photocurable layer; and    -   f) washing away uncured portions of the photocurable layer to        reveal the relief image in the compressible printing plate.

In an alternate embodiment, the invention is directed to a method ofpreparing a compressible relief image printing plate comprising thesteps of:

-   -   a) securing a photographic negative to a glass platen, wherein        the photographic negative has opaque areas corresponding to a        reverse of a desired relief image;    -   b) covering the photographic negative with a transparent cover        sheet;    -   c) casting a photocurable layer onto the cover sheet;    -   d) laminating a compressible foam layer to the liquid        photocurable layer;    -   e) exposing the photocurable layer to actinic radiation through        the compressible layer to cure a portion of the photocurable        layer to create a cured floor in the photocurable layer;    -   f) exposing the photocurable layer to actinic radiation through        the photographic negative to form the relief image in the        photocurable layer; and    -   g) washing away uncured portions of the photocurable layer to        reveal the relief image in the compressible printing plate.

In this embodiment, the compressible foam layer is formed by:

-   -   a) casting a layer of a photocurable composition comprising a        polyurethane resin and thermoplastic microspheres to a desired        thickness on a glass platen; and    -   b) exposing the layer of photocurable composition to actinic        radiation from both sides of the layer of photocurable        composition to thoroughly cure the layer.

The polyurethane resin is preferably an acrylate or methacrylatepolyurethane resin.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is had to thefollowing description taken in connection with the accompanying figures,in which:

FIG. 1 is an illustration of a printing plate manufacturing processaccording to the present invention.

FIG. 2 is a partial cross-sectional schematic view of a printing plateproduced by the process of the present invention.

Also, while not all elements may be labeled in each figure, all elementswith the same reference number indicate similar or identical parts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to an improved compressibleflexographic printing plate that minimizes the time it takes to readythe plate for press usage. The novel process of the invention uses acompressible layer that comprises a liquid polyurethane resin(preferably acrylate or methacrylate polyurethane resin) withthermoplastic microspheres dispersed therein. The microspheres serve tocreate voids in the urethane material, allowing for compressibilitywithin the layer.

According to the process of the invention, a printing plate comprising aphotopolymer layer and a compressible layer can be prepared having noadhesive or tie layer therebetween. Plates prepared according to theinventive process thus avoid the problems associated with using anadhesive, a tape or a tie layer to adhere the photopolymer layer to thecompressible layer.

The ideal formulation of the printing plate/compressible layer system isaccomplished using conventional liquid photopolymer platemakingequipment, and is analogous to making a capped printing plate. FIG. 1illustrates a portion of the flexographic printing plate manufacturingprocess for creating the compressible printing plates of the invention.FIG. 2 illustrates a printing plate 20 prepared by the novel process ofthe invention.

The method of manufacturing compressible flexographic printing plates 20according to the present invention typically comprises the steps of:

-   -   a) securing a photographic negative 22 to a glass platen 32,        wherein the photographic negative 22 has opaque areas        corresponding to a reverse of a desired relief image;    -   b) covering the photographic negative 22 with a transparent        cover sheet 24 to protect the photographic negative 22 (or other        image-bearing transparency);    -   c) creating a bi-layer photocurable system on the cover sheet 24        by casting a first photocurable layer 26 on the cover sheet 24        and then casting a photocurable compressible layer 28 directly        on top of the first photocurable layer 26;    -   d) exposing the bi-layer photocurable system to a source of        actinic radiation 38 through the photocurable compressible layer        28 to cure the photocurable compressible layer 28 and a portion        of the first photocurable layer 26 to create a cured floor in        the first photocurable layer 26;    -   e) exposing the bi-layer photocurable system to another source        of actinic radiation 36 through the photographic negative 22 to        form the relief image 40 (shown in FIG. 2) in the first        photocurable layer 26; and    -   f) washing away uncured portions of the first photocurable layer        26 to reveal the relief image 40 in the compressible printing        plate 20.

The first photocurable layer 26 is cast onto the cover sheet 24 byreleasing a liquid photocurable composition from a resin reservoir, andcasting the composition onto the transparent cover film 24 with the aidof a leveling blade.

Optionally, the plate system can be a traditional capped system, whichrequires the casting of a very thin layer of photopolymer resin beforethe first photocurable layer 26 is cast, followed by the compressiblelayer 28.

The total thickness of the first photocurable layer 26 and thecompressible layer 28 are determined by the amount of resin cast, thesettings of the doctor blade used to laminate the resin across theglass, and the shims used to hold a fixed distance between the upper andlower glass. The compressible printing plate 20 of the invention mayfurther comprise a platebacking material (support layer) 30, which isgenerally a polyester film coated with an adhesion promoting layer, andis used to lock in the dimensional stability of the material. Theplatebacking material 30 can be the same material that is used to makeconventional flexographic printing plates.

A glass platen 32 is positioned between the photographic negative 22 anda first source of actinic radiation 36. A second source of actinicradiation 38 is positioned above the platebacking material 30. In apreferred embodiment, the first source of actinic radiation 36 and thesecond source of actinic radiation 38 comprises a bank of fluorescenttubes. A glass platen 34 is positioned between the platebacking material30 and the second source of actinic radiation 38 to provide a means forcontrolling thickness uniformity of the first photocurable layer 26, bylowering the glass platen 34 prior to exposure to rest on shims and makecontact with the platebacking material 30.

Upon exposure to actinic radiation, the photocurable resin polymerizesand changes from a liquid to a solid state, to form both a floor and araised relief image 40 in the first photocurable layer 26.

The compressible layer 28 of the invention generally comprises a liquidpolyurethane resin having microspheres uniformly dispersed therein. Thecompressible layer 28 may also contain a photoinitiator. Thepolyurethane resin is preferably an acrylate or methacrylatepolyurethane resin.

The choice of the microspheres is important to the success of thisinvention. The microspheres are preferably of uniform size and/oruniform particle distribution and can exist as either expanded orunexpanded particles. In a preferred embodiment, expanded microspheresare used, due to the heat required to effectively mix the microspheresinto the viscous polyurethane methacrylate resin composition. The weightpercent of the microspheres in the compressible composition typicallyranges from about 0.5% to about 5.0% by weight of the resin formulation,but is not preferably from about 1.0% to 2.5% by weight.

Regardless of whether the microsphere is expanded or unexpanded, themicrospheres generally consist of a thermoplastic shell encapsulating ahydrocarbon. The shell of the microsphere is typically a copolymer ofacrylonitrile and vinylidene chloride or methacrylonitrile, and thehydrocarbon inside the shell is typically isobutane or isopentane. Thereare a number of commercial sources for thermoplastic microspheres.EXPANCEL® is a trade name for microspheres available from NobleIndustries. Dualite and Micropearl polymeric microspheres are availablefrom Pierce & Stevens Corporation.

Preferably, both the first photocurable layer 26 and the compressiblelayer 28 comprise polyurethane di(meth)acrylate resins.

Liquid polyurethane methacrylate resins are common feedstocks for liquidphotopolymer platemaking. Due to the similarities between the foam andthe base resin chemistries, both being polyurethane di(meth)acrylatesand containing similar monomers, adhesion is enhanced. The physicalproperties of the compressible foam layer 28 can be altered through theappropriate choice of polyurethane prepolymer, together with theappropriate choice and proportion of the acrylate/methacrylate monomers.Using photoinitiators suitable for thick film imaging or high opticaldensity imaging, i.e., a pigmented/heavily dyed system, the foam can bethoroughly cured under ultraviolet light to lock the microspheres into acrosslinked matrix, and also to lock in the desired physical propertiesof the foam.

The first photocurable layer 26 generally has a thickness of about 0.030to about 0.250 inches, and is chosen for its compatibility with thecompressible layer 28 such that after the curing process, the firstphotocurable layer 26 and the compressible layer 28 remain distinctentities yet bond together tightly enough (without the aid of anadhesive) such that the layers will not separate or fracture during theprinting process. The novel process of the invention produces achemically fused printing plate 20 is produced by the diffusion of thefirst photocurable layer 26 and the compressible layer 28 into eachother when the layers are exposed to actinic radiation.

A further advantage to the process of the invention is that thethickness of the compressible layer 28 can be adjusted to meet the needsof the printing job by adjusting the platemaking parameters. Incontrast, current compressible printing plate systems require thestorage of multiple thicknesses of the compressible materials to meetvarious needs of different print jobs. The compressible layers 28 formedin the process of the instant invention generally have a thickness ofabout 0.015 in. to about 0.125 in., depending on the type of substrateto be printed. The overall printing plate thickness typically rangesfrom about 0.045 in to about 0.155 in.

Suitable liquid photocurable materials include unsaturated polymericcompounds such as polyesters, polyethers, polyene-thiol compositions,polyurethanes, terminally unsaturated homopolymers and copolymers ofbutadiene, isoprene, chloroprene, styrene, isobutylene, and ethylene inwhich the terminal unsaturation is attached to the polymer through acombination of at least two ether, thioether, ester, keto, or amidegroups, used in combination with a photoinitiator. Exemplary liquidphotocurable materials are disclosed in U.S. Pat. No. 3,661,575 toKetley et al., U.S. Pat. No. 4,332,873 to Hughes et al., and U.S. Pat.No. 4,266,007 to Hughes et al., the subject matter of each of which isincorporated herein by reference in its entirety. Other liquidphotocurable materials would also be known to one skilled in the art.

The liquid photopolymerizable (or photocurable) layer(s) can include anyof the known photopolymers, monomers, initiators, reactive ornon-reactive diluents, fillers, and dyes. The term “photocurable” refersto a solid composition which undergoes polymerization, cross-linking, orany other curing or hardening reaction in response to actinic radiationwith the result that the unexposed portions of the material can beselectively separated and removed from the exposed (cured) portions toform a three-dimensional or relief pattern of cured material. Preferredphotocurable materials include an elastomeric compound, an ethylenicallyunsaturated compound having at least one terminal ethylene group, and aphotoinitiator.

The hardness of the compressible layer 28 and the first photocurablelayer 26 is achieved by adjusting the composition of each layer so thatthe layers will have the desired relative hardness after curing. This istypically accomplished by those skilled in the art by controlling theamount of cross-linking which occurs during photopolymerization. Theamount of cross-linking in a polymer composition is directlyproportional to its hardness. Those skilled in the art typically controlthe amount of cross-linking by choosing or making polymers withdifferent degrees of unsaturation. The more unsaturation within apolymer composition, the more cross-linked the polymer will be oncecured and, hence, the harder it will be. This and other methods ofachieving different: degrees of hardness and other desired physical andchemical characteristics of cured photopolymer resins comprising reliefimage flexographic printing plates are well known lo those skilled inthe art and are discussed in detail in U.S. Pat. No. 4,332,873 to Hugheset al. and U.S. Pat. No. 3,990,897 to Zuerger et al., the subject matterof each of which is herein incorporated by reference in its entirety.Hardness is typically measured according to the procedure set forth inASTM standard D 2240-91 (Standard Test Method for RubberProperty—Durometer Hardness).

The photocurable layers of the invention should cross-link (cure) and,thereby, harden in at least some actinic wavelength region. As usedherein, actinic radiation is radiation capable of effecting a chemicalchange in an exposed moiety. Actinic radiation includes, for example,amplified (e.g., laser) and non-amplified light, particularly in the UVand infrared wavelength regions. Preferred actinic wavelength regionsfor curing the photocurable materials of the invention are from about:250 nm to about 450 nm, more preferably from about 300 nm to about 400nm, even more preferably from about 320 nm to about 380 nm. One suitablesource of actinic radiation is a UV lamp, although other sources aregenerally known to those skilled in the art.

The compressible plate 20 of the invention is processed as a normalliquid photopolymer is traditionally processed—including the steps ofreclaim, washout, post exposure, drying and light finishing to removethe unexposed photopolymer layer. The finished plate is then mounted ona cylinder of a printing press. The resulting plate material can then beprocessed. The end result is a pre-mounted printing plate/compressiblelayer system that is ready to go to press.

In an alternate approach, two separate casting and exposure stages areutilized. The foam layer is made separately from the complete system bysimply casting the desired thickness of foam onto the glass and exposingthe plate thoroughly; both a back exposure and a face exposure aredesired for thorough through-cure. The foam “plate” can then be used asthe backing layer in a subsequent platemaking step, by laminating thefoam as is traditionally done for simple polyester backings, followed byback and face exposures. This aids to lock in adhesion and to helpimaging by providing some relief layer with the base resin. Creatingsome relief will ease the ability of light scatter to occur from thefoam layer through the base layer.

In this approach, the method generally comprises the steps of:

-   -   a) securing a photographic negative to a glass platen, wherein        the photographic negative has opaque areas corresponding to a        reverse of a desired relief image;    -   b) covering the photographic negative with a transparent cover        sheet;    -   c) casting a first photocurable layer onto the cover sheet;    -   d) laminating a compressible foam layer to the liquid        photocurable layer;    -   e) exposing the first photocurable layer to actinic radiation        through the compressible layer to cure a portion of the first        photocurable layer to create a cured floor in the first        photocurable layer;    -   f) exposing the first photocurable layer to actinic radiation        through the photographic negative to form the relief image in        the first photocurable layer; and    -   g) washing away uncured portions of the first photocurable layer        to reveal the relief image in the compressible printing plate.

In this alternate approach, the compressible foam layer is formed by:

-   -   a) casting a layer of a photocurable composition comprising a        polyurethane (meth)acrylate resin and thermoplastic microspheres        to a desired thickness on a glass platen; and    -   b) exposing the layer of photocurable composition to actinic        radiation from both sides of the layer of photocurable        composition to thoroughly cure the layer.

This is an alternate approach from both the end-user's point of view andfrom the manufacturer.

As is readily apparent, the manufacturer has the choice of providingliquid foam (the first approach) or the cured foam substrate (the secondapproach) to the consumer. In the preferred embodiment, the liquid foamis provided, as the one step system is more time-efficient and morequality-efficient, yielding a better adhesion of the layers of theprinting plate and better imaging of the printing plate.

One of the major advantages of the process of the present invention liesin its time and material savings steps. No separate foam material isneeded, only the microsphere-containing resin. In addition, an adhesivelayer is not required for laminating the printing plate onto thecompressible layer. Furthermore, since the curing of the foam and baseresin occurs simultaneously, a chemically fused system is created as aresult of diffusion of one layer into the other. In this way, theprocess of the invention is analogous to the formation of cappedprinting plates, in which the thin layer cap is slightly crosslinkedinto the base resin, although retaining much of its own physicalproperties as a secondary layer.

A typical formulation for the compressible composition useful in thepractice of this invention is:

-   -   62 parts polyurethane methacrylate oligomer    -   1 part photoinitiator (such as Ingacure 651 or 819 available        from Ciba Geigy)    -   0.1 part butylated hydroxy toluene    -   7 parts 2-ethoxy ethoxy ethyl acrylate    -   5 parts diethylene glycol dimethacrylate    -   14 parts polypropylene glycol monomethacrylate    -   7 parts lauryl methacrylate    -   1 part Expancel 551 DE-80 Microspheres (avail from Noble        Industries)

1. A method of manufacturing a compressible flexographic printing platecomprising the steps of: a) securing a photographic negative to a glassplaten, wherein the photographic negative has opaque areas correspondingto a reverse of a desired relief image; b) covering the photographicnegative with a transparent cover sheet; c) creating a photocurablesystem on the cover sheet by casting at least one photocurable layer onthe cover sheet and then casting a photocurable compressible layer ontop of at least one photocurable layer; d) exposing the photocurablesystem to actinic radiation through the photocurable compressible layerto cure the photocurable compressible layer and a portion of the atleast one photocurable layer to create a cured floor in the firstphotocurable layer; e) exposing the photocurable system to actinicradiation through the photographic negative to form the relief image inthe at least one photocurable layer; and f) washing away uncuredportions to reveal the relief image in the compressible printing plate.2. The method according to claim 1, wherein the compressible layercomprises a liquid polyurethane methacrylate resin having microspheresuniformly dispersed therein.
 3. The method according to claim 2, whereinthe compressible layer further comprises a photoinitiator.
 4. The methodaccording to claim 1, wherein the microspheres are selected from thegroup consisting of expanded microspheres and unexpanded microspheres.5. The method according to claim 4, wherein the microspheres areexpanded microspheres.
 6. The method according to claim 1, wherein thecompressible layer comprises about 1 percent to about 2.5 percent byweight of the microspheres.
 7. The method according to claim 1, whereinthe at least one photocurable layer and the compressible layer bothcomprise polyurethane di(meth)acrylate resins.
 8. The method accordingto claim 7, wherein a chemically fused printing plate is produced by thediffusion of the photocurable layer and the compressible layer into eachother when the layers are exposed to actinic radiation.
 9. A method ofmanufacturing a compressible flexographic printing plate comprising thesteps of: a) securing a photographic negative to a glass platen, whereinthe photographic negative has opaque areas corresponding to a reverse ofa desired relief image; b) covering the photographic negative with atransparent cover sheet; c) casting a photocurable layer onto the coversheet; d) laminating a compressible foam layer to the photocurablelayer; e) exposing the photocurable layer to actinic radiation throughthe compressible layer to cure a portion of the first photocurable layerto create a cured floor in the photocurable layer; f) exposing thephotocurable layer to actinic radiation through the photographicnegative to form the relief image in the photocurable layer; and g)washing away uncured portions of the photocurable layer to reveal therelief image in the compressible printing plate; wherein thecompressible foam layer is formed by i. casting a layer of aphotocurable composition comprising a polyurethane (meth)acrylate resinand thermoplastic microspheres to a desired thickness on a glass platen;and ii. exposing the layer of photocurable composition to actinicradiation from both sides of the layer of photocurable composition tothoroughly cure the layer.
 10. The method according to claim 9, whereina chemically fused printing plate is produced by the diffusion of thefirst photocurable layer and the compressible layer into each other whenthe layers are exposed to actinic radiation.
 11. The method according toclaim 9, wherein the photocurable layer comprises polyurethanedi(meth)acrylates resins.